<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">On Sep 6, 2016, at 6:06 PM, Jonathan Hull via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><div><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div class=""><div style="white-space:pre-wrap" class="">I'm not entirely sure on my position, though. To be convinced otherwise, I'd need to see a compelling real-world use case that demonstrates all of the following:<br class=""><br class="">- Safety: perhaps, with protocols, unlike class inheritance, it is almost always safe to make these kinds of changes unanticipated by the original author--it would be good to see evidence either way<br class=""></div></div></blockquote><div class=""><br class=""></div><div class="">You may find this paper interesting:</div><div class=""><a href="http://scg.unibe.ch/archive/papers/Scha02bTraits.pdf" class="">http://scg.unibe.ch/archive/papers/Scha02bTraits.pdf</a></div><div class=""><br class=""></div><div class="">It discusses traits, which are basically Swift’s protocols, plus the ability to handle conflicts. It discusses at length the issues that arise with other systems.</div><div class=""><br class=""></div><div class="">This is a very common problem that only a few programming languages have found successful solutions to. I would also point you to Eiffel’s model for multiple inheritance (select, rename, undefine, export). I think if we keep working on it, we can find a uniquely swift-feeling solution which solves the issue :-)</div></div></div></div></blockquote><br class=""></div><div>Here’s another obscure paper coming from the world of C++, see section 3.5/4.1:</div><div><a href="http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.48.129" class="">http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.48.129</a></div><div><br class=""></div><div>Not a syntax that we would want to emulate, but it’s the same idea in different clothes. The Swift implementation model should support implementing something along these lines, but it would be a purely additive feature.</div><div><br class=""></div><div>-Chris</div><br class=""></body></html>